The prevent invention relates to data processing devices and semiconductor devices. More specifically, the present invention relates preferably to a semiconductor device in which a plurality of processors are composed of integrated circuits, in particular, CMOS circuits which change in power consumption depending on the operational states thereof, and which semiconductor device allows the processors to exhibit those performance well while minimizing the power consumption for the entire semiconductor chip.
With the expansion of portable device markets including a cellular phone market, there is growing importance of semiconductor chips operable even at a low power. It is desirable that the maximum power consumption, the average power consumption, the standby power consumption, and power distribution across a semiconductor chip should be each controlled to a low level when the semiconductor chip is operated.
The maximum power consumption serves as a factor in determining the power that is fed to a semiconductor chip. A smaller power supply capacity than the maximum power consumption will result in a voltage drop and therefore a chip malfunction. Consequently a chip with large maximum power consumption naturally requires a power supply system with a high power supply capacity, thus resulting in an increase in portable device costs and weights. The maximum power consumption serves as a factor in designing the heat dissipation capacity of a package or system. A large maximum power consumption will require a package or system with a high heat dissipation capacity. Also such a package or system will lead to an increase in portable device costs and weights.
The average power consumption also has a direct influence on the service life or weight of a portable device battery. The larger the average power consumption, the shorter the service life of a battery will be. A longer service life of a battery will therefore raise a problem of a heavier battery.
The standby power consumption will be important in systems whose power supply cannot be turned OFF when a portable device is not in use or which usually are used with the power supply turned ON. If, for example, a cellular phone is turned OFF when not in use, the cellular phone cannot receive incoming calls. For this reason, a cellular phone is, in many cases, always in the standby mode so that the phone can operate immediately after receiving an incoming call. If a cellular phone uses much power when in the standby mode, the phone can be kept in the standby mode for a short period of time.
Power distribution across a chip has an influence on the design of a chip power line and a power supply pin, and a heat dissipation capacity. A large local power consumption will result in a voltage drop and therefore a malfunction if a chip does not have a sufficient capacity to handle a voltage from a power line and power supply pin for power supply thereto. Large local heat generation and an insufficient heat dissipation capacity will also result in a temperature rise and therefore malfunction.
For power control for an integrated circuit, Japanese Patent Laid-open No. 10-69330 titled “Logical circuit and method for avoiding a hot spot on an integrated circuit,” for example, discloses a technique for dividing an entire integrated circuit into a plurality of functional units and monitoring heat generation for each functional unit to control local heat generation to below an allowable level. Heat is generated when power consumption leads to Joule heat. Heat generation control to an allowable level or below means indirect control of a local maximum power consumption across a chip, i.e., power distribution control to an allowable level or below. The patent document states that this control therefore reduces a possibility of an obstacle due to overheat, thus allowing a reduction in power consumption across an entire chip.
In addition, Japanese Patent Laid-open No. 10-91298 titled “Self power monitor and control circuit for microprocessor functional units” states that a power sensing circuit is provided for each functional unit and a functional unit of interest is made to operate in a low power mode when the power consumption thereof exceeds a predetermined value.
There are typically two concepts for control of power across a semiconductor chip. One concept involves intensive control of power consumption for each functional module (“a functional unit” in Japanese Patent Laid-open Nos. 10-69330 and 10-91298) while the other involves local distributed power control as described in Japanese Patent Laid-open Nos. 10-69330 and 10-91298.
In recent years process miniaturization has caused a plurality of processor cores and many modules such as various IPs to be mounted on a single chip. Intensive power consumption control therefore requires power distribution to many modules, thus resulting in more power consumption information to be considered and a longer distance over which a signal travel. This makes control signal production a complicated and time-consuming processing.
In addition, the combination of various IPs to fabricate a system LSI requires a designer familiar with the power-related characteristics of all IPs to design a power control module for intensive control every time a system LSI is fabricated. This design is extremely difficult if many IPs are mounted on a single chip.
Only local power consumption control is important for power distribution across a chip, one of the power-related considerations mentioned above. A larger power consumption value cannot be set for one module even if each of the other modules located far away from the module has low power consumption. On the other hand, a larger value can be set for one module if each of the surrounding modules has low power consumption. Therefore, it can be said that intensive control of other modules located far away from one module is excessive and wasteful control from the viewpoint of power distribution across a chip.
The above patent documents cover local power control in units of function units. The techniques described in the above documents allow proper power consumption control in functional units, but no consideration is given to power consumption across an entire chip. In other words, setting an allowable power consumption value of up to an original maximum power consumption to each module will result in power consumption beyond the maximum power consumption across an entire chip.
On the other hand, assume that allowable power consumption lower than an original maximum power consumption is set to each module from the view point of control of the maximum power consumption across an entire chip by means of local power consumption control and trade-off. In this case, individual modules will not be capable of operating at the highest performance at which they have the original maximum power consumption.
In addition, each module usually operates on approximately the average power and the modules as a whole tend to operate on power that is much smaller than the total sum of the allowable powers even if some of the modules operate on set allowable powers. Therefore individual modules may not be capable of perform properly due to power consumption. It is therefore necessary to get the idea of allowing power consumption so that each module can perform sufficiently, taking into power consumption for other modules.